The present invention relates to a shaft sealing ring composed of a basic body made of an elastomer material, a housing member which can be reinforced with metal, and a sealing lip which can be reinforced by a spring, the sealing lip having a sealing edge adapted to be pressed circumferentially against the surface of a shaft to be sealed by the sealing ring. When the shaft sealing ring is installed on a shaft, its sealing edge is radially deformed and contacts the shaft surface, thereby forming a seal, the contact region between the seal and the shaft surface being referred to hereafter as a running zone having a defined contact width.
The sealing effect of a shaft sealing ring as defined, for example, in DIN (German Industrial Standard) 3760, is based on the fact that the sealing edge is urged by radial compression forces against the shaft surface to be sealed. The deformation of the rubber material against the shaft surface in the region of the sealing edge produces a running zone which has a defined contact width. Upon rotation of the shaft, a liquid film flows underneath a side of the sealing edge which is in contact with the fluid medium, such that the sealing edge does not directly contact the shaft surface. Although the liquid can flow underneath the sealing edge and form a lubricating film, it does not flow to the side of the seal which is in contact with the air environment.
A sealing theory published in ATZ Automobiltechnische Zeitschrift 88 (1986), pages 39-45, explains this phenomenon. The shaft sealing ring has a sealing edge with first and second walls that form the sealing edge. In a cross-sectional view taken through this shaft sealing ring, the first and second walls forming the sealing edge appear as generally linear portions which are inclined relative to the shaft surface and to each other such that they meet at the sealing edge. In this example, the wall which is in contact with the fluid medium is disposed at an angle relative to the shaft surface which is in a range between 40.degree. and 50.degree., while the other wall which is in contact with the air environment is disposed at an angle relative to the shaft surface which is in a range between 20.degree. and 30.degree., so that, in the installed condition of the shaft sealing ring about the shaft, the compression forces in the sealing edge are distributed asymmetrically relative to the cross section of the sealing lip. The deformation of the shaft sealing ring in its installed condition is, therefore, also asymmetrical along its axial direction. This structure permits the development of a hydrodynamic conveying effect from the side of the sealing edge contacting the environment (e.g., air) to the side of the sealing edge contacting the fluid medium.
For economic reasons, presently manufactured shaft sealing rings predominantly have pressed-on sealing edges. Subsequent working by grinding or stamping is therefore not necessary. The consequence of this manufacturing process is that the two walls forming the sealing edge do not meet at an entirely sharp edge, and instead meet at a transition region having an arcuate cross-sectional outline having a constant radius of curvature. When installed, a shaft sealing ring according to the prior art, having a pressed-on sealing edge, exhibits an initial axial distribution of compression whose maximum lies approximately in the center of the width of the contact area in the running zone. Only after the seal has been worn in, will the angles of the two walls forming the sealing edge have an influence on the distribution of the compression forces. During the wearing-in process, the angles of inclination of the two walls forming the sealing edge are not determinative of the presence of the hydrodynamic sealing effect, and instead the transition region between the angled walls performs the sealing function.